Hallux valgus and plantar pressure loading: the

AbstractBackground: Hallux valgus (HV), a common structural foot deformity, can cause foot pain and lead to limitedmobility. The purpose of this study was to evaluate differences in plantar pressure and force during gait by HVstatus in a large population-based cohort of men and women.Methods: A trained examiner performed a validated physical examination on participants feet and recorded thepresence of hallux valgus and other specific foot disorders. Each foot was classified into one of four mutuallyexclusive groups based on the foot examination. Foot groups were: (i) HV only, (ii) HV and at least one additionalfoot disorder (FD), (iii) no HV but at least one other FD, and (iv) neither HV nor FD (referent). Biomechanical data forboth feet were collected using Tekscan Matscan. Foot posture during quiet standing, using modified arch index(MAI), and foot function during gait, using center of pressure excursion index (CPEI), were calculated per foot.Further, walking scans were masked into eight sub-regions using Novel Automask, and peak pressure andmaximum force exerted in each region were calculated.Results: There were 3205 participants, contributing 6393 feet with complete foot exam data and validbiomechanical measurements. Participants with HV had lower hallucal loading and higher forces at lesser toes aswell as higher MAI and lower CPEI values compared to the referent. Participants with HV and other FDs were alsonoted to have aberrant rearfoot forces and pressures.Conclusions: These results suggest that HV alters foot loading patterns and pressure profiles. Future work shouldinvestigate how these changes affect the risk of other foot and lower extremity ailments.

BackgroundHallux valgus (HV), a structural foot deformity oftenresulting in a reactive soft tissue bunion, can cause foot painand limited mobility [1]. Women are twice as likely to havethis condition [2,3] and older adults have a higher prevalenceof HV (23% aged 1825 years versus 35.7% over age 65 years)[4]. Footwear has also been implicated in the development ofHV; especially shoes with higher heels or improper fit [5].The degree to which foot anatomy or biomechanics influence HV is poorly understood. In a 2012 systematic review and meta analysis, Nix et al. reported that the firstintermetatarsal angle and first metatarsal protrusions* Correspondence: hannan@hsl.harvard.edu

Equal contributors1Institute for Aging Research at Hebrew Senior Life, 1200 Centre Street,Boston, MA, USA2Beth Israel Deaconess Medical Center, Boston, MA, USAFull list of author information is available at the end of the article

distance were significantly associated with hallux valgus,

but also noted that a number of radiographic factors werenot significantly associated with hallux valgus [6]. Archheight is noted as an area of interest in clinical models ofhallux valgus [7], which often cite low arches as a contributing factor. However, past research has yielded inconsistent results [6]. While Nguyen et al. found a significantassociation between a clinical assessment of pes planusand hallux valgus in men [2], Kilmartin et al. reported norelation between arch height and hallux valgus when usingan arch index [8]. Similarly, studies are inconsistent regarding whether a curved joint head was [9] or was not[10] associated with HV.Studies that report on plantar pressure distributionsfor individuals with and without HV are also inconclusive. For example, loading at the hallux may be reduced[11-13], increased [14], or unaffected [15] by the presence of HV. These studies were limited by small sample

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sizes [14-16] and narrow age ranges [15,17], as well as

exclusions of severe clinical cases [14], men [18] , andfeet with multiple foot disorders [18].Prior studies are limited by conflicting results, smallsample sizes, and consideration of hallux valgus in isolation of concurrent foot disorders. Addressing theselimitations can impact clinical decision making andevaluation of treatment strategies. The purpose of thisstudy is to describe plantar pressures and forces in alarge epidemiologic, population-based study of olderadults and to investigate whether these measures differbetween those with and without HV and other footdeformities. We hypothesized that the presence of HV isassociated with decreased loading under the hallux andresultant offloading under the forefoot.

MethodsStudy population

Study participants were members of the Framingham

Foot Study [18], a population-based study comprisedof three cohorts: Framingham Original Cohort,Framingham Offspring Cohort and a community sampledrawn from the town of Framingham, MA, USA [18].Briefly, the Framingham Original Cohort was derived in1948 from a two-thirds population-based sample of thetown of Framingham, MA, USA, while the FraminghamOffspring cohort was composed of a sample of the adultchildren and spouses of the Original Cohort. Membersof these cohorts between 20022008 were included inthe Framingham Foot study along with a newly recruitedcommunity sample. The Framingham community sample was recruited via census-based, random digit-dial ofambulatory residents who were age 50 or older. TheFramingham Foot Study was approved by the Institutional Review Boards at Hebrew SeniorLife and BostonUniversity. All study participants provided written, informed consent prior to enrolment. Between 2002 and2008, Foot Study participants received a physical andbiomechanical assessment of their feet. For this analysis,only Framingham Foot Study participants with completefoot biomechanical data and foot disorder data wereincluded.

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multiple examiners yielded kappa values >0.85 (all p <

0.01), and all domains demonstrated excellent interobserverand intraobserver reliability [19,20]. Presence of HV (yes/no) was defined as a 15 or greater abduction of the halluxwith respect to the first metatarsal. While the participantwas standing, the examiner compared the angle of the hallux to an illustration of a 15 angle printed on a laminatedpage, and recorded hallux valgus as present if the angle waslarger than the illustration. Hallux valgus, hammer toes,claw toes, and overlapping toes were assessed duringweight-bearing stance. Hallux rigidus was measured whilethe participant was non-weight bearing and was consideredpresent if the hallux was frozen or rigid during attemptedpassive movement by the examiner. All foot disorders (FD)were recorded as present or absent.Each foot was classified into one of four mutuallyexclusive groups based on the physical examination.The foot groups were defined as: (i) hallux valgus only(HV-only), (ii) HV and at least one additional foot disorder (HV + FD), (iii) no HV but at least one other footdisorder (no HV-FD only), and (iv) no-HV and no-FD(referent group).Age, sex and weight were also recorded at the time ofexamination. Weight was measured to the nearest halfpound using a standardized balance beam scale andconverted to Newtons.Plantar pressure data collection

Plantar pressure data were collected using a Tekscan

Matscan (Tekscan Inc., Boston MA) pressure mat with acapture rate of 40 Hz, which was sufficient for the typeof data collected and has moderate to good reliability[21]. A scan of each participant in quiet, bipedal stancewas collected. Additionally, participants were instructedto walk at a self-selected pace across the mat. A singlepressure scan of each foot was recorded using the twostep method [22], which entails the participants steppingon the pressure map on the second step. The two-stepmethod has been shown to be as reliable as data collection using the mid-gait approach [22]. The time constraints associated with a large epidemiological studyallowed recording of a single walking trial.

Hallux valgus and other foot disorders

Plantar pressure analysis and outcome measures

A podiatric-trained examiner performed a validated

physical examination on participants feet and recordedthe presence of specific foot disorders including halluxvalgus, hallux rigidus, claw toes, hammers toes, andoverlapping toes [2]. The validity of the foot exam waspreviously evaluated in a sample of elderly residents bycomparing podiatry clinic findings to the results fromthe trained study examiners. There was excellent agreement for HV as well as other foot disorders that wereincluded in the foot examination. A comparison of

Galica et al. Journal of Foot and Ankle Research 2013, 6:42

Figure 2 Calculation of the center of pressure excursion index

(CPI) and the modified arch index (MAI) in the FraminghamFoot Study, 20022008. Used with permission by Arthritis Care &Research; John Wiley & Sons, Inc.

Figure 1 The eight region foot mask used to analyze Matscan

plantar pressure scans in the Framingham Foot Study,20022008.

modified arch index (MAI), a measure of foot structure

[24], were calculated for each foot. CPEI is related toclinical foot type and was defined as the excursion of thecenter of pressure from a constructed line connectingthe first and last points of a center of pressure curvemeasured in the distal tertile of the foot and normalizedby the foots width [23]. Lower CPEI values indicate amore pronated foot during gait, whereas higher CPEIvalues indicate more supination (Figure 2). MAI, calculated from the static weight-bearing stance scan was calculated by dividing each foot, not including the toes,lengthwise into three equal segments. The pressureunder the middle third of the foot was divided by thepressure under the entire foot to yield the MAI [24].Previous work has shown that MAI was inversely associated with navicular height, with higher MAI values indicating a lower arch [25].Statistical analysis

Means and standard deviations, or frequencies, where

appropriate, were calculated for the overall population,and separately by foot group. A per-foot analysis usinglinear regression was used to determine the associationbetween each biomechanical measure and foot group,both crude and adjusted (age, sex, and weight[Newtons]). Generalized Estimating Equations (GEE)were used to account for the correlation between rightand left foot of the same person. The dependent

variables were peak pressure and maximum force in

each of the foot regions, along with CPEI and MAI. Results were considered statistically significant at p < 0.05.P-values from the linear regression models were adjustedfor the 8 comparisons made within the mask in modelsof peak pressure and maximum force using a Bonferronicorrection for multiple comparison testing. P-valuesfrom models of CPEI and MAI were not adjusted. Theresults presented account for the correction for multipletesting. All statistical analyses were conducted using theSAS statistical analysis package, version 9.3 (SAS Institute, Cary, NC).

ResultsPopulation

There were 3205 participants, contributing 6393 feet

with complete foot exam data and valid biomechanicalmeasurements (Figure 3). The average age was 66 yearsand 56% of the sample was female (Table 1).Maximum forces

Statistically significant differences in maximum force

under the hallux were seen in both HV groups (i.e., HVOnly, HV + FD), but not in the No-HV + FD after adjustment for age, sex, and weight (Table 2). In additionto reduced loading under the hallux, the HV-only grouphad increased loading under the lesser toes in bothcrude and adjusted models. Though crude associationssuggested decreased loading in additional regions, theHV-only group was not significantly different from thereferent group at the other masked regions in adjustedmodels. By comparison, the HV + FD group had significantly reduced loading under both the lateral forefoot

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in both the medial and lateral rearfoot. In the No-HV +

FD group, a similar increase in pressure was observedunder the lesser toes, but no changes were observed inany other masked region.Center of pressure excursion index (CPEI) and modifiedarch index (MAI)

CPEI was significantly reduced in both the HV-only and

HV + FD groups, but was not statistically significantlydifferent in the No-HV + FD group. MAI, by comparison, was not significantly different in the HV-only group,but it was higher than the referent in the HV + FD andthe No-HV + FD groups. These associations weremaintained in both crude and adjusted models.

Figure 3 Flow of data for the participants included in the

analysis of Framingham Foot Study data, 20022008.

and lateral rearfoot in addition to the aforementioned

reduction under the hallux in both crude and adjustedmodels. After adjustment, the HV + FD group did notdiffer significantly from the referent in any other regions.The No-HV + FD group did not have any statisticallysignificant differences in force in the adjusted modelsrelative to the referent group, though there were significant crude associations. No significant differences wereseen for any of the foot groups at the lateral or medialmidfoot.

DiscussionThe purpose of this study was to evaluate the differencesin plantar pressure and force during gait by hallux valgus(HV) status in a large population-based cohort of menand women. Our results show that loading in the halluxregion was lower in participants with HV-only and inthose with HV and other foot disorders, compared tothose who had neither. All groups (HV-only, HV + FD,and FD-only) had greater loading or pressure in thelesser toe regions when compared to the referent. TheHV + FD group also had lower lateral rearfoot maximum force and lateral and medial peak pressures relative to the referent. Furthermore, feet in the HV + FDgroup were more likely to display a lower center of pressure excursion index (CPEI) values, higher modified archindex (MAI) values, and reduced lateral rearfoot forceand lowered rearfoot peak pressures compared to thereferent group. These results suggest that feet with HVhave altered loading patterns and pressure profiles thatmay put them at greater risk of other foot and lower extremity ailments.

Peak pressures

There were no significant differences in peak pressure

observed in the HV-only group in crude or adjustedmodels, but several differences were noted in the HV +FD group. In this group, in both crude and adjustedmodels, peak pressure was significantly reduced underthe hallux, increased under the lesser toes, and reduced

Hallux and lesser toes

Our study showed reduced force under the hallux in

both HV groups (i.e., HV-only and HV + FD), but not inthe No-HV + FD group. Pressure was also reducedunder the hallux in the HV + FD group. While reducedpressure under the hallux in those with hallux valgus

*Data reported as mean standard deviation, unless otherwise noted.

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Table 2 Distributions of foot biomechanical variables in each of the four foot groups, Framingham foot study,20022008Variable

No Hallux Valgus / Nofoot disorder (referent)

Hallux Valgus only

Hallux Valgus +foot disorder

Foot disorder only

78.4 (39.70)

64.9 (41.72)*

47.7 (33.47)*

70.4 (42.28)

Maximum Force (N)

HalluxLesser ToesLateral Forefoot

41.1 (27.12)249.7 (102.50)

45.3 (38.04)*

40.7 (25.91)

38.1 (27.83)

229.8 (110.81)

225.7 (104.30)

Medial Forefoot

132.9 (72.03)

Lateral Midfoot

116.5 (94.35)

108.3 (93.37)

109.5 (76.57)

124.4 (112.22)

Medial Midfoot

18.8 (24.62)

21.0 (32.87)

20.0 (24.17)

21.6 (27.84)

Lateral RearfootMedial Rearfoot

175.6 (63.30)

123.1 (63.02)

206.2 (84.81) *

163.9 (59.92)

116.4 (62.89)

151.9 (51.41) *

130.3 (76.12)

167.1 (70.77)

196.5 (68.11)

181.8 (65.06)

172.6 (56.38)

191.9 (73.32)

218.6 (102.01)

212.0 (106.44)

171.3 (99.38)*

206.0 (106.66)

138.8 (77.36)

144.5 (87.82)

148.3 (71.93)*

152.2 (90.16)*

Peak Pressure (kPa)

HalluxLesser ToesLateral Forefoot

251.3 (88.12)

240.3 (89.11)

Medial Forefoot

212.8 (101.25)

206.5 (99.94)

207.2 (86.07)

222.0 (104.89)

Lateral Midfoot

108.8 (64.45)

106.3 (74.1)

107.8 (61.02)

113.1 (72.42)

231.5 (71.15)

249.6 (88.87)

Medial Midfoot

74.4 (53.20)

73.5 (65.18)

68.1 (39.27)

73.4 (55.17)

Lateral Rearfoot

216.8 (80.05)

208.2 (80.42)

200.4 (62.83)*

213.1 (83.86)

Medial Rearfoot

230.0 (85.98)

222.3 (84.72)

215.3 (67.21)*

233.1 (92.31)

14.7 (8.07)

13.0 (8.00)*

12.5 (7.74)*

14.5 (8.00)

0.112 (0.095)*

0.116 (0.099)*

Center of Pressure Excursion Index

Modified Arch Index

0.102 (0.0809)

0.098 (0.079)

Means (standard deviations).

CPEI = center of pressure excursion index.= significantly different from referent group in crude model at p < 0.05 with Bonferroni adjustment.*= significantly different from referent group in adjusted model (age, weight, sex) at p < 0.05 with Bonferroni adjustment.

has been seen in previous studies [13,17], this result has

not been reported consistently [26]. Past studies havealso observed no significant difference in loading of thehallux [15], as well as an increase in pressure under thehallux [14]. The conflicting findings noted by MartinezNova et al. [14] could be due to the inclusion of onlymild cases of hallux valgus and a comparatively smaller,younger cohort (mean age 54.7 years). Biomechanicalstudies have suggested a number of mechanisms to explain the reduced loading in the hallux region in feet withHV, including first ray hypermobility. In this model thefirst metatarsal gives way, resulting in an offloading of thehallux onto other aspects of the foot such as the secondmetatarsal [9,16,17,27]. The offloading of the hallux maybe due to the reduced ability of the hallux to bear load[27], or an adaptation to pain. Correspondingly, we foundreduced loading at the hallux region with HV, while maximum force in the lesser toe area was increased in theHV-only group. As this study is cross-sectional is it unclear if the differences in halluca l loading associated withHV are a result of HV or causative of it.We also noted higher peak pressure under the lessertoes in those feet with other structural foot disorders

(i.e., HV + FD and No-HV + FD groups). As noted

above, the offloading of the hallux may be due to its reduced ability to bear load [27], or as an adaptation topain. In the HV + FD and No-HV + FD groups, the lackof significant changes in force at the lesser toes points toa different explanation. As the other foot disorders considered in this study are primarily structural disorders ofthe toes, it is possible that the contact area under thetoes is reduced in these two groups as a result of otherfoot disorders, which can explain increases in pressuredespite the lack of significant changes in force in thosewith the other structural foot disorders.Forefoot

Prior studies of surgical patients have also reported that

HV is associated with lower loading at the 1st metatarsophalangeal joint (MTPJ) [11,12]. This reduced loadinghas been theorized to result from an elevation of the 1stMPJ during gait, which limits the load this area is ableto accept in those with HV [16,17,28]. Studies in nonclinical groups by comparison have noted an increasedload at the 1st MTPJ [15,16,26]. In this analysis, therewere no differences with adjusted models in the medial

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forefoot in any of the foot disorder groups. As the

masking used in this study did not differentiate betweenthe individual metatarsals, it possible that the offloadingof the first metatarsal head was offset by increased forceon the 2nd MPJ. Nonetheless, no significant differenceswere seen in the medial forefoot, even in feet with HV.While no changes were observed in the medial forefoot,the HV + FD group had significantly reduced loading inthe lateral half of the forefoot. Lower force in the lateralforefoot has not been previously attributed to HV. Oneexplanation for the lower loading in the lateral forefootcould be a more pronated foot during gait, which is typically thought to be associated with HV. This hypothesiswas supported by the significantly lower CPEI value observed in the groups with HV.

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foot type, which has been associated with a lower CPEI

[23]. This observation is further supported in the HV +FD group by higher MAI values, indicating a lower archin this group relative to the referent. These results offersupport that HV is associated with differences in footstructure and function. Further research is needed to expand these novel findings.Strengths and limitations

Center of pressure excursion index (CPEI) and modified

arch index (MAI)

While this study provides important insights into the

foot biomechanics associated with hallux valgus, thereare several limitations. As the study design was crosssectional, causal relations cannot be inferred. Nonetheless, associations between foot groups and loading offeran epidemiological view of common loading profiles inthose with HV and foot disorders. Only a single walkingtrial for each foot was recorded, which may have increased measurement error. However, random errorwould only serve to obscure weaker relations in thesedata rather than create false positive associations [33].Moreover, the large study sample greatly mitigates thisissue, as it is more than sufficiently powered even with asingle scan [34].As a common mask was used to define foot regionsfor all pressure scans, it is possible that foot regions maynot have correlated exactly with the anatomical locationof the corresponding metatarsals in some cases. Tomore accurately define foot regions, it may be useful infuture studies to align anatomical foot structure fromspiral X-ray tomography with plantar pressure data asdescribed by Hastings et al. [35].Although studies have previously addressed the topicof plantar loading in HV, our study was unique in that itwas population-based and included both men andwomen and individuals with additional foot disorders.Recent studies of plantar loading have been limited byrelatively small samples (~ 300 participants) [14,16].Thus, the current study with over 3000 participants withinformation on multiple foot disorders may offer insightsinto the associations of HV that smaller studies cannot.Our study which included participants with HV andadditional structural foot disorders, a typical exclusionfor other HV studies [14], provides an understanding ofhow foot function is influenced when HV is coupledwith additional structural foot disorders.

Biomechanical modelling of HV has reported associations of pes planus foot type with the etiology of HV[28]. However, clinical and biomechanical studies of HVhave not yielded consistent results to implicate a particular foot type with HV [7,32]. In this current study, asmaller CPEI was observed in both HV-only and HV +FD groups. This indicates that participants with HVhave a more pronated foot during gait relative to the referent group and may be more likely to have a pes planus

ConclusionsAlthough the pathogenesis of HV is complex, a betterunderstanding of HV and its clinical outcomes can beachieved by evaluating the validity of theoretical, kinematic, and radiographic results through plantar pressureloading. Plantar loading can assess the functional impactof a structural deformity as seen during gait, and thisstudy has confirmed several key results in a population-

Rearfoot

Of the studies that have reported on the midfoot and

rearfoot regions, there was no subdivision of these areasinto a medial and lateral section [16,29], and only onestudy [29] showed a difference in either the midfoot orrearfoot pressures between feet with and without HV.Nyska et al. noted that feet prior to undergoing corrective surgery for HV displayed lower rearfoot pressurerelative to those without the foot disorder [29]. In ourstudy, a lower maximum force in the lateral rearfoot andlower rearfoot peak pressure were observed in the HV +FD group. A similar association of a medial to lateralloading pattern in people with rheumatoid arthritis suggests the rearfoot and forefoot may be coupled and therearfoot may play a role in forefoot complications [30].The medial to lateral loading pattern arises from a valgus rearfoot alignment and leads to excessive stress atthe subtalar joint and forefoot region [31]. Althoughrearfoot alignment was not evaluated in this currentstudy, the lower values of the CPEI noted in the groupswith HV suggest that they displayed a valgus rearfootalignment [23]. In short, these results suggest that therearfoot may be an important factor in the etiology andtreatment of HV. This novel aspect of our findingswould need further investigation of these patterns of results in future studies.

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based sample of adult men and women with HV.

Namely, a lower hallucal loading was seen in participants with HV, with greater loading at the toes. HV andfoot disorders was also associated with altered rearfootforces, which given prior evidence suggesting forefootcomplications are associated with rearfoot disorders,suggests that the rearfoot should be considered in etiology and treatment of HV and forefoot complications.In addition, lower CPEI and higher MAI values were associated with HV, confirming results from studies thathave described foot pronation and lower arch structurein feet with HV. Prospective studies are needed to elucidate of the etiology of HV and structural disorders in relation to plantar pressure loading. Moreover, longitudinalstudies of HV and foot disorders can track plantar pressure and loading changes that develop over time.

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3.4.5.6.

7.8.9.10.11.

12.Competing interestsThe authors have no competing interests to report.Authors contributionsAMG contributed to the analysis and interpretation of data and drafted theoriginal manuscript. TJH contributed to the analysis and interpretation ofdata and drafted the original manuscript. ABD carried out the statisticalanalyses, contributed to the interpretation of data and the revision of themanuscript. JLR participated in the interpretation of data and the draftingand revision of the manuscript. HJH participated in the study conceptionand design and provided critical revision of the manuscript for intellectualcontent. VAC made substantial contributions to the drafting and revision ofthe manuscript. MTH conceived of the study, was responsible for theacquisition of data, contributed to the analysis and interpretation of data,and provided critical revision of the manuscript for intellectual content.All authors read and approved the final manuscript.Authors informationAndrew M Galica and Thomas J Hagedorn share first authorship on thismanuscript.AcknowledgementsThe authors acknowledge the Framingham Foot Study research team andstudy participants for the contribution of their time, effort, and dedication.Funding for this project was provided by: the National Institute of Arthritisand Musculoskeletal and Skin Diseases and National Institute on Aging(AR047853). This work was derived from the Framingham Heart Study of theNational Heart Lung and Blood Institute of the National Institutes of Healthand Boston University School of Medicine. This work was supported bythe National Heart, Lung and Blood Institute's Framingham Heart Study(Contract No. N01-HC-25195).

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